Imaging Apparatus

This application is a continuation of application No. PCT/JP2024/003999, filed on Feb. 7, 2024, and claims the benefit of priority from the prior Japanese Patent Application No. 2023-036632, filed on Mar. 9, 2023, the entire content of which is incorporated herein by reference.

The present disclosure relates to an imaging apparatus.

A configuration using a multi-plate prism is known as a multi-plate imaging apparatus configured to capture a common incident light with a plurality of sensors. For example, a configuration in which each of a visible light and an infrared light is imaged by using a spectroscopic prism is known (see, for example, Patent Literature 1).

In certain applications, two sensors that image light of the first wavelength and one sensor that images light of the second wavelength may be used in combination. When the wavelength is separated by configuring the first splitting surface of a three-plate prism as a dichroic mirror, there is a restriction that requires a sensor that captures the second wavelength be placed on the exit surface of the first prism. When the wavelength is separated by configuring the first splitting surface of the three-plate prism as a half mirror and configuring the second splitting surface as a dichroic mirror, a sensor that captures the second wavelength can be placed on the exit surface of the second prism or the third prism. However, the intensity of light at the second wavelength is reduced to half as a result of transmission through the half mirror of the first splitting surface.

An imaging apparatus according to an embodiment of the present disclosure includes: a light splitting element that includes a first splitting surface adapted to split an incident light into a first reflected light and a first transmitted light and a second splitting surface adapted to split the first transmitted light into a second reflected light and a second transmitted light; a first sensor that images the first reflected light; a second sensor that images the second reflected light; and a third sensor that images the second transmitted light. The first splitting surface is configured to partially transmit a first wavelength with a first transmittance, partially reflect the first wavelength with a first reflectivity, and transmit a second wavelength different from the first wavelength with a second transmittance having a larger value than both the first transmittance and the first reflectivity. The second splitting surface is configured to transmit one of the first wavelength and the second wavelength and reflect the other of the first wavelength and the second wavelength.

Optional combinations of the aforementioned constituting elements, and mutual substitution of constituting elements and implementations of the present disclosure between methods, apparatuses, systems, etc. may also be practiced as additional modes of the present disclosure.

The invention will now be described by reference to the preferred embodiments. This does not intend to limit the scope of the present invention, but to exemplify the invention.

A description will be given below of embodiments of the present disclosure with reference to the drawings. Specific numerical values shown in the embodiments are by way of example only to facilitate the understanding of the invention and should not be construed as limiting the disclosure unless specifically indicated as such. Those elements in the drawings not directly relevant to the present disclosure are omitted from the illustration.

schematically shows a configuration of an imaging apparatusaccording to the embodiment. The imaging apparatusincludes a first sensor, a second sensor, a third sensor, and a light splitting element. The imaging apparatusis a so-called three-plate camera and is configured to split an incident lightusing the light splitting elementand capture an image with each of the first sensor, the second sensor, and the third sensor.

The light splitting elementincludes a first prism, a second prism, and a third prism. The light splitting elementis a so-called three-plate prism. The first prismincludes a first incidence surface, a first splitting surface, and a first exit surface. The second prismincludes a second incidence surface, a second splitting surface, and a second exit surface. The third prismincludes a third incidence surfaceand a third exit surface. An air gap is provided between the first splitting surfaceand the second incidence surface.

The incident lightincident on the first incidence surfaceis split into a first reflected lightand a first transmitted lightby the first splitting surface. The first reflected lightreflected by the first splitting surfaceis totally reflected internally by the first incidence surfaceand is then transmitted through the first exit surfaceto travel toward the first sensor. The first transmitted lighttransmitted through the first splitting surfaceis split into a second reflected lightand a second transmitted lightby the second splitting surface. The second reflected lightreflected by the second splitting surfaceis totally reflected internally by the second incidence surfaceand is then transmitted through the second exit surfaceto travel toward the second sensor. The second transmitted lighttransmitted through the second splitting surfaceis transmitted through the third incidence surfaceand the third exit surfaceto travel toward the third sensor.

The first sensoris a sensor that captures the first wavelength. One of the second sensorand the third sensoris a sensor that captures the first wavelength. The other of the second sensorand the third sensoris a sensor that captures the second wavelength different from the first wavelength. Thus, two of the first sensor, the second sensor, and the third sensorare sensors that capture the first wavelength, and the remaining one of the first sensor, the second sensor, and the third sensoris a sensor that captures the second wavelength.

The first wavelength represents, for example, visible light, and the second wavelength represents, for example, infrared light. The first wavelength may represent infrared light, and the second wavelength may represent visible light. The specific wavelength of the first wavelength and the second wavelength is not particularly limited, and any wavelength in the wavelength range from ultraviolet light to infrared light can be selected. Further, at least one of the first wavelength and the second wavelength may have a predetermined wavelength range. In the case that the first wavelength or the second wavelength represents visible light, for example, the first wavelength or the second wavelength may mean a part or the entirety of the visible wavelength range from red to blue.

The first sensor, the second sensor, and the third sensorare visible light sensors that capture visible light or infrared light sensors that capture infrared light. Each of the visible light sensor and the infrared light sensor includes an imaging element including a plurality of pixels. A two-dimensional image sensor such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor) can be used as the imaging element.

The visible light sensor may be a color image sensor in which red (R), green (G), and blue (B) color filters are provided for each pixel. The visible light sensor may be a polarization sensor in which a plurality of types of polarizers having different polarization directions are provided for each pixel. The visible light sensor may be an event-based vision sensor (EVS) that outputs an image in which only those pixels for which a brightness change is detected are extracted. The infrared light sensor may be a thermal image sensor for capturing a thermal image. The infrared light sensor may be a distance image sensor that measures a distance to an object according to the ToF (Time of Flight) scheme.

The first splitting surfaceis configured to partially transmit and reflect the first wavelength and entirely transmit the second wavelength different from the first wavelength. In other words, the first splitting surfacehas partial transparency and partial reflectiveness for the first wavelength and total transparency for the second wavelength. The first splitting surfaceis configured to be a half mirror with respect to the first wavelength and substantially total transparent (i.e., non-reflective) with respect to the second wavelength. Each of the first transmittance Tand the first reflectivity Rat the first wavelength on the first splitting surfaceis set within a range between a predetermined lower limit value (e.g., 30%, 35%, 40%, or 45%) to a predetermined upper limit value (e.g., 70%, 65%, 60%, or 55%) and is preferably 40% or more and 50% or less. The second transmittance Tat the second wavelength on the first splitting surfaceis larger than the first transmittance Tand the first reflectivity Rat the first wavelength on the first splitting surfaceand is larger than a predetermined upper limit value (e.g., 70%). The second transmittance Tat the second wavelength on the first splitting surfaceis, for example, 90% or more and preferably 95% or more.

The second splitting surfaceis configured to entirely transmit one of the first wavelength and the second wavelength and to entirely reflect the other of the first wavelength and the second wavelength. In other words, the second splitting surfacehas total transparency for one of the first wavelength and the second wavelength and total reflectiveness for the other of the first wavelength and the second wavelength. The second splitting surfaceis a so-called dichroic mirror, which selectively transmits one of the first wavelength and the second wavelength and selectively reflects the other. The transmittance at one of the first wavelength and the second wavelength on the second splitting surfaceis larger than the first transmittance Tand the first reflectivity Rat the first wavelength on the first splitting surfaceand is larger than a predetermined upper limit value (e.g., 70%). The transmittance at one of the first wavelength and the second wavelength on the second splitting surfaceis, for example, 90% or more and preferably 95% or more. The reflectivity at the other of the first wavelength and the second wavelength on the second splitting surfaceis larger than the first transmittance Tand the first reflectivity Rat the first wavelength on the first splitting surfaceand is larger than a predetermined upper limit value (e.g., 70%). The reflectivity at the other of the first wavelength and the second wavelength on the second splitting surfaceis, for example, 90% or more and preferably 95% or more.

Each of the first splitting surfaceand the second splitting surfacecan be comprised of, for example, a dielectric multilayer mirror. The first splitting surfaceand the second splitting surfacehaving the desired wavelength characteristics as described above can be realized by adjusting the refractive index and the thickness of each layer constituting the dielectric multilayer film.

In the three-plate prism as shown in, the installation space allowance varies depending on the position of the sensor. Since the third sensoris arranged at a position that does not interfere with the light splitting element, much installation space allowance is available so that a sensor having a relatively large sensor size Dcan be arranged. On the other hand, the second sensoris in close proximity to the third prismand has a small installation space allowance so that only a sensor having a relatively small sensor size Dcan be arranged. The first sensorhas more installation space allowance than the second sensor, but it is necessary to consider interference with the third prismso that the first sensorhas a smaller installation space allowance than the third sensor. Therefore, the sensor size Dthat the first sensorcan have is larger than the sensor size Dthat the second sensorcan have and is smaller than the sensor size Dthat the third sensorcan have (i.e., D>D>D).

A description will now be given of the advantage provided by the embodiment with reference to comparative examples.

is a table showing exemplary optical characteristics of the imaging apparatusaccording to the embodiment and the comparative examples. In the example of, the transmittance in the case of substantially total transmittance (i.e., non-reflection) is defined to be 100%, the transmittance in the case of substantially total reflection (that is, non-transparency) is defined to be 0%, and the transmittance in the case of partial transmittance and reflection is defined to be 50%, for ease of understanding. With regard to the intensity of light incident on each of the first sensor, the second sensor, and the third sensor, the light intensity of the incident lightis defined to be 100%, and the light loss due to the passage through the light splitting elementis ignored.

In the first embodiment and the second embodiment, the transmittance at the first wavelength on the first splitting surfaceis 50%, and the transmittance at the second wavelength on the first splitting surfaceis 100%. In the first embodiment, the transmittance at the first wavelength on the second splitting surfaceis 100%, and the transmittance at the second wavelength on the second splitting surfaceis 0%. In the second embodiment, contrary to the first embodiment, the transmittance at the first wavelength on the second splitting surfaceis 0%, and the transmittance at the second wavelength on the second splitting surfaceis 100%.

In the first embodiment, the intensity of light at the first wavelength incident on each of the first sensorand the third sensoris 50%, and the intensity of light at the second wavelength incident on the second sensoris 100%. In the first embodiment, therefore, the first sensorand the third sensorare sensors that capture the first wavelength, and the second sensoris a sensor that captures the second wavelength.

In the second embodiment, the intensity of light at the first wavelength incident on each of the first sensorand the second sensoris 50%, and the intensity of light at the second wavelength incident on the third sensoris 100%. In the second embodiment, therefore, the first sensorand the second sensorare sensors that capture the first wavelength, and the third sensoris a sensor that captures the second wavelength.

In the comparative example, a common half mirror and a common dichroic mirror are used in combination in the first splitting surfaceand the second splitting surface.

In comparative example 1, the first splitting surfaceis a dichroic mirror, and the second splitting surfaceis a half mirror. In comparative example 1, the transmittance at the first wavelength on the first splitting surfaceis 100%, and the transmittance at the second wavelength on the first splitting surfaceis 0%. In comparative example 1, the transmittance at the first wavelength on the second splitting surfaceis 50%, and the transmittance at the second wavelength on the second splitting surfaceis 50%.

In comparative example 1, the intensity of light at the first wavelength incident on each of the second sensorand the third sensoris 50%, and the intensity of light at the second wavelength incident on the first sensoris 100%. In comparative example 1, therefore, the second sensorand the third sensorare sensors that capture the first wavelength, and the first sensoris a sensor that captures the second wavelength.

In comparative example 1, the intensity of light at the first wavelength incident on each of the two sensors that capture the first wavelength can be maximized (e.g., to 50%), and the intensity of light at the second wavelength incident on the one sensor that captures the second wavelength can be maximized (e.g., to 100%). In comparative example 1, there is a restriction on arrangement that requires that the sensor for capturing the second wavelength be the first sensor.

In comparative example 2 and comparative example 3, the first splitting surfaceis a half mirror, and the second splitting surfaceis a dichroic mirror. In comparative example 2 and comparative example 3, the transmittance at the first wavelength on the first splitting surfaceis 50%, and the transmittance at the second wavelength on the first splitting surfaceis 50%. In comparative example 2, the transmittance at the first wavelength on the second splitting surfaceis 100%, and the transmittance at the second wavelength on the second splitting surfaceis 0%. In comparative example 3, the transmittance at the first wavelength on the second splitting surfaceis 0%, and the transmittance at the second wavelength on the second splitting surfaceis 100%.

In comparative example 2, the intensity of light at the first wavelength incident on each of the first sensorand the third sensoris 50%, and the intensity of light at the second wavelength incident on each of the first sensorand the second sensoris 50%. In comparative example 3, the intensity of light at the first wavelength incident on each of the first sensorand the second sensoris 50%, and the intensity of light at the second wavelength incident on each of the first sensorand the third sensoris 50%.

In comparative example 2, the sensor that captures the second wavelength can be the first sensoror the second sensor, and, in comparative example 3, the sensor that captures the second wavelength can be the first sensoror the third sensor. Therefore, there is little restriction on arrangement. In comparative example 2 and comparative example 3, the intensity of light at the second wavelength incident on the sensor that captures the second wavelength is about 50% so that the intensity of light at the second wavelength incident on the sensor that captures the second wavelength cannot be maximized (e.g., to 100%).

According to the embodiment, on the other hand, the intensity of light at the first wavelength incident on each of the two sensors that capture the first wavelength can be maximized (e.g., to 50%), and the intensity of light at the second wavelength incident on the one sensor that captures the second wavelength can also be maximized (e.g., to 100%), as in comparative example 1. Further, the sensor that captures the second wavelength can be arranged as the second sensoror the third sensorby using either the first embodiment or the second embodiment. According to the embodiments, therefore, the degree of freedom in sensor arrangement can be improved as compared to comparative example 1, and the intensity of light at the first wavelength or the second wavelength incident on the three sensors can be maximized as compared to comparative examples 2-3. According to the embodiments, maximization of the intensity of light incident on the plurality of sensors and the degree of freedom in the arrangement of the plurality of sensors can be achieved at the same time.

In the case of the first embodiment, the sensor that captures the second wavelength is the second sensorso that, for example, it is possible to use large sensors as the two sensors that capture the first wavelength. In the case of the second embodiment, the sensor that captures the second wavelength is the third sensorso that, for example, it is possible to use a large sensor as the sensor that captures the second wavelength.

Hereinafter, exemplary embodiments relating to specific wavelength characteristics of the first splitting surfaceand the second splitting surfacewill be described.

is a graph schematically showing the wavelength characteristics of a first splitting surfaceA and a second splitting surfaceA according to the first exemplary embodiment. The first exemplary embodiment ofrepresents a version of the first embodiment described above in which the first wavelength is a visible light wavelength of 700 nm or less and the second wavelength is an infrared light wavelength of 800 nm or more.

On the first splitting surfaceA, the first transmittance at the first wavelength (visible light) is about 50% (e.g., 45%-50%), and the second transmittance at the second wavelength (infrared light) is about 100% (e.g., 95%-100%). On the first splitting surfaceA, the first reflectivity at the first wavelength (visible light) is about 50% (e.g., 45%-50%), and the second reflectivity at the second wavelength (infrared light) is about 0% (e.g., 0%-5%).

On the second splitting surfaceA, the transmittance at the first wavelength (visible light) is about 100% (e.g., 95%-100%), and the transmittance at the second wavelength (infrared light) is about 0% (e.g., 0%-5%). On the second splitting surfaceA, the reflectivity at the first wavelength (visible light) is about 0% (e.g., 0%-5%), and the reflectivity at the second wavelength (infrared light) is about 100% (e.g., 95%-100%).

In the first exemplary embodiment, about 50% of the light intensity of the incident lightat the first wavelength (visible light) can be incident on each of the first sensorand the third sensor, and about 100% of the light intensity of the incident lightat the second wavelength (infrared light) can be incident on the second sensor.

In the first exemplary embodiment, the first sensorand the third sensorare visible light sensors, and the second sensoris an infrared light sensor. According to the first exemplary embodiment, the light intensity of visible light incident on each of the first sensorand the third sensorcan be maximized, and the light intensity of infrared light incident on the second sensorcan be maximized. The first exemplary embodiment is effective when the sensor size of the two visible light sensors is sought to be increased.

According to the first exemplary embodiment, the first sensorcan be a color image sensor, the second sensorcan be a distance image sensor, and the third sensorcan be a polarization sensor or an EVS, for example. The sensor size available to polarization sensors and EVSs may be limited as compared to other sensors, and polarization sensors and EVSs may have a relatively large sensor size. According to the first exemplary embodiment, the third sensorwith the largest installation space allowance can be a polarization sensor or an EVS. Further, a distance image sensor may have a smaller number of pixels than other sensors and may have a relatively small sensor size. According to the first exemplary embodiment, the second sensorwith the smallest installation space allowance can be a distance image sensor. Thereby, the first sensorwith a larger installation space allowance as compared to the second sensorcan be a color image sensor. Consequently, a color image sensor with a larger sensor size can be employed as compared to a case where the second sensoris a color image sensor.

is a graph schematically showing the wavelength characteristics of a first splitting surfaceB and a second splitting surfaceB according to the second exemplary embodiment. The second exemplary embodiment ofrepresents a version of the first embodiment described above in which the first wavelength is an infrared light wavelength of 800 nm or more and the second wavelength is a visible light wavelength of 700 nm or less.

On the first splitting surfaceB, the first transmittance at the first wavelength (infrared light) is about 50% (e.g., 45%-50%), and the second transmittance at the second wavelength (visible light) is about 100% (e.g., 95%-100%). On the first splitting surfaceB, the first reflectivity at the first wavelength (infrared light) is about 50% (e.g., 45%-50%), and the second reflectivity at the second wavelength (visible light) is about 0% (e.g., 0%-5%).

On the second splitting surfaceB, the transmittance at the first wavelength (infrared light) is about 100% (e.g., 95%-100%), and the transmittance at the second wavelength (visible light) is about 0% (e.g., 0%-5%). On the second splitting surfaceB, the reflectivity at the first wavelength (infrared light) is about 0% (e.g., 0%-5%), and the reflectivity at the second wavelength (visible light) is about 100% (e.g., 95%-100%).

In the second exemplary embodiment, about 50% of the light intensity of the incident lightat the first wavelength (infrared light) can be incident on each of the first sensorand the third sensor, and about 100% of the light intensity of the incident lightat the second wavelength (visible light) can be incident on the second sensor.

In the second exemplary embodiment, the first sensorand the third sensorare infrared light sensors, and the second sensoris a visible light sensor. According to the second exemplary embodiment, the light intensity of infrared light incident on each of the first sensorand the third sensorcan be maximized, and the light intensity of visible light incident on the second sensorcan be maximized. The second exemplary embodiment is effective when the size of the two infrared light sensors is sought to be increased as much as possible. In the second exemplary embodiment, the first sensorcan be a distance image sensor, the second sensorcan be a color image sensor, and the third sensor can be a thermal image sensor, for example.

is a graph schematically showing the wavelength characteristics of a first splitting surfaceC and a second splitting surfaceC according to the third exemplary embodiment. The third exemplary embodiment ofrepresents a version of the second embodiment described above in which the first wavelength is a visible light wavelength of 700 nm or less and the second wavelength is an infrared light wavelength of 800 nm or more.

The first splitting surfaceC is the same as the first splitting surfaceA according to the first embodiment. On the first splitting surfaceC, the first transmittance at the first wavelength (visible light) is about 50% (e.g., 45%-50%), and the second transmittance at the second wavelength (infrared light) is about 100% (e.g., 95%-100%). On the first splitting surfaceC, the first reflectivity at the first wavelength (visible light) is about 50% (e.g., 45%-50%), and the second reflectivity at the second wavelength (infrared light) is about 0% (e.g., 0%-5%).

The second splitting surfaceC represents a version of the second splitting surfaceA according to the first embodiment in which the reflectivity and the transmittance are inverted. On the second splitting surfaceC, the transmittance at the first wavelength (visible light) is about 0% (e.g., 0%-5%), and the transmittance at the second wavelength (infrared light) is about 100% (e.g., 95%-100%). On the second splitting surfaceC, the reflectivity at the first wavelength (visible light) is about 100% (e.g., 95%-100%), and the reflectivity at the second wavelength (infrared light) is about 0% (e.g., 0%-5%).

In the third exemplary embodiment, about 50% of the light intensity of the incident lightat the first wavelength (visible light) can be incident on each of the first sensorand the second sensor, and about 100% of the light intensity of the incident lightat the second wavelength (infrared light) can be incident on the third sensor.

In the third exemplary embodiment, the first sensorand the second sensorare visible light sensors, and the third sensoris an infrared light sensor. According to the third exemplary embodiment, the light intensity of visible light incident on each of the first sensorand the second sensorcan be maximized, and the light intensity of infrared light incident on the third sensorcan be maximized. The third exemplary embodiment is effective when the size of the one infrared light sensor is sought to be increased as much as possible. In the third exemplary embodiment, the first sensorcan be a polarization sensor or an EVS, the second sensorcan be a color image sensor, and the third sensor can be a thermal image sensor or a distance image sensor, for example.